Since yesterday, JPEG images are being saved. Is it just me?

Since yesterday, I noticed that the generated images are being saved as JPEGs in addition to PNGs. It’s kind of annoying, because previously only PNGs were saved. I also feel like the generation is taking longer than usual—maybe because of the extra saving process?

Is there a way to disable JPEG output and go back to PNG-only saving?

Thanks in advance!